The detection of immune responses to pathological organisms or the detection of pathogen-related proteins or other antigens in the serum of patients has benefited greatly from immunoassay development over the last 15 years. In one form of immunoassay, monoclonal or polyclonal antibodies that recognize the immunoglobulins of another species are used. These reagents, known as anti-species antibodies are labelled, typically with a fluorochrome or enzyme, and used to detect antigen binding by immunoglobulins found in immune serum. In another form of immunoassay, known as the sandwich assay, antibodies directed against pathogen proteins are used to capture antigen from, for example, patients' serum or cerebrospinal fluid (CSF), that is then detected by the binding of another, labelled antibody directed against the same antigen. All of these assays, however, are limited by the sensitivity of detection of the bound immunoglobulin and require fairly large concentrations, on a molar basis, of labelled reagent.
More recent assays utilize nucleic acid amplification methods, such as the polymerase chain reaction (PCR) for DNA amplification, to detect very low levels of nucleic acid. Nucleic acid amplification methods can allow the detection of pathological agents in serum or in the environment at levels well below that of immunoassay detection. Such techniques, however, are often very sensitive to contamination from the environment and require prior knowledge of the nucleic acid sequence of interest in order to identify a portion of the nucleic acid and amplify it for detection. Nucleic acid amplification requires that there be nucleic acid present to amplify and detect and is, therefore, of no or limited utility when the compound of interest is a protein, carbohydrate, or other non-nucleic acid molecule. Further improvements in the effectiveness and sensitivity of compound detection in a sample are desirable, and the present invention addresses the existing problems and provides related benefits.